Semiconductor memory device and method for testing same

ABSTRACT

A semiconductor memory device includes data input/output terminals (DQ 0  to DQ 31 ), a memory cell array  122,  and a data latch circuit  111  for temporarily latching data captured from the data input/output terminals and writing the data in the memory cell array with a delay in a normal write operation. The device also includes a test mode in which the data latch circuit latches data read to the data input/output terminals in a read operation and writes previously latched data in the memory cell array without newly latching data from the data input/output terminals in a write operation.

REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of the priority ofJapanese patent application No. 2008-199843, filed on Aug. 1, 2008, thedisclosure of which is incorporated herein in its entirety by referencethereto.

FIELD OF THE INVENTION

The present invention relates to a semiconductor memory device and amethod for testing same.

BACKGROUND

In recent years, in response to demands from the market for smallermobile devices, a system in which DRAMs and processor chips are stackedin the same package is being developed. In such system, since signalterminals that transmit data between the DRAMs and the processors areconnected by wirings inside the package, it is difficult to inspect theDRAM chips directly through external terminals after sealed in thepackage. For this reason, such DRAMs need to be inspected for qualityinspection before mounted on a package, that is, at the wafer level. Inorder to reduce costs for testing, the DRAM wafer inspection is carriedout on 200 chips or more by simultaneously probing signal terminals froma memory tester. Thus, the number of signals assigned to each of thememory chips is limited by the total number of signal terminals of thememory tester. Meanwhile, in the system configuration of such mobiledevice, for better performance, the data input/output terminals of theDRAM is being extended to ×16, ×32, and ×64 to increase the datatransmission rate. Thus, conventionally, DRAMs used for such purposeshave a test mode, aiming to realize a wafer inspection with a smallnumber of signal terminals and a certain number of data input/outputterminals even when measuring many chips simultaneously.

Patent Document 1 discloses a double-data-rate synchronous dynamicrandom access memory (hereinafter referred to as DDR-SDRAM) thatconducts a test with 8 input/output terminals (DQ0, DQ4, DQ8, DQ12,DQ16, DQ20, DQ24, and DQ28) among 32 data input/output terminals (DQ0 toDQ31) (see FIGS. 21 to 23, FIGS. 27 and 28, and paragraphs 0005 to 0009,0172 to 0189, and 0207 to 0221 of Patent Document 1; or FIGS. 21 to 23,FIGS. 27 and 28, and column 1 line 40 to column 2 line 8, column 19 line46 to column 21 line 5, and column 22 line 62 to column 24 line 7 ofU.S. Pat. No. 6,324,118).

Patent Document 1: Japanese Patent Kokai Publication No.JP-P2000-76853A, which corresponds to U.S. Pat. No. 6,324,118

SUMMARY

The entire disclosure of Patent Document is incorporated herein byreference thereto.

The following is an analysis by the present invention.

With the test mode as disclosed in the above Patent Document 1, even inthe case of a DRAM chip having many data input/output terminals (DQterminals), it is possible to inspect the memory cell array by probingonly a small number of the data input/output terminals. However,according to studies made by the present inventors, with this testmethod, a normal operation in which reading from/writing to a DRAM isconducted via all the DQ terminals described above cannot be tested.Especially, in recent years, the operating frequency of a DRAM is beingincreased, which is also the case with those DRAMs stacked withprocessor chips in the same package as described in the above system. Insuch cases, high-speed operation of input/output circuits in a normaloperation needs to be checked when inspecting the wafer.

A semiconductor memory device according to a first aspect of the presentinvention comprises: a data input/output terminal; a memory cell array;and a data latch circuit configured to temporarily latch data capturedfrom the data input/output terminal and write the data in the memorycell array with a delay in a normal write operation. Further, thesemiconductor memory device has a test mode in which the data latchcircuit latches data read to the data input/output terminal in a readoperation and writes previously latched data in the memory cell arraywithout newly latching data from the data input/output terminal in awrite operation.

In addition, a semiconductor memory device according to a second aspectof the present invention is a synchronous semiconductor memory devicecomprising: a data input/output terminal; a memory cell array; and adata latch circuit configured to temporarily latch data captured fromthe data input/output terminal in synchronization with a data strobesignal supplied from the outside and write the data in the memory cellarray with a delay when a normal write command is executed. Thesynchronous semiconductor memory device further comprises an internaldata strobe signal generation circuit and has a test mode in which thedata latch circuit latches data read to the data input/output terminalin synchronization with an internal data strobe signal generated by theinternal data strobe signal generation circuit when a read command isexecuted and writes previously latched data in the memory cell arraywithout newly latching data from the data input/output terminal when awrite command is executed.

A semiconductor memory device according to a third aspect of the presentinvention comprises: a data input/output terminal; a memory cell array;and a data latch circuit configured to temporarily latch data capturedfrom the data input/output terminal and write the data in memory cellarray later. The semiconductor memory device has: a first command forlatching data captured from the data input/output terminal in the datalatch circuit in synchronization with a strobe signal supplied from theoutside and writing the latched data in the memory cell array insynchronization with an internal clock; a second command for readingdata from the memory cell array to the data input/output terminal andlatching the read data in the data latch circuit; and a third commandfor writing data stored in the data latch circuit in the memory cellarray without newly capturing data from the data input/output terminalinto the data latch circuit.

A semiconductor memory device test method according to a fourth aspectof the present invention is a method for testing a semiconductor memorydevice comprising: a plurality of data input/output terminals; and amemory cell array in which one address is composed of multiple bits thatcan be read/written in parallel with the use of the plurality of datainput/output terminals and having a test mode in which data read inparallel from the multiple-bit memory cell array to the plurality ofdata input/output terminals is written in parallel in a multiple-bitaddress different from the read address. The test is conducted bywriting first and second data in first and second regions, respectively,in the memory cell array in advance, using the test mode, writing thesecond data read from the second region in the first region, and readingthe data from the first region after the second data is written in thefirst region.

The meritorious effects of the present invention are summarized asfollows.

According to the present invention, a read/write test, includinginput/output circuits between the memory cell array and the datainput/output terminals, can be conducted efficiently.

Other features and advantages of the present invention will be apparentfrom the following description taken in conjunction with theaccompanying drawings, in which like reference characters designate thesame or similar parts throughout the figures thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an overall block diagram of a semiconductor memory deviceaccording to one example of the present invention.

FIG. 2 shows a block diagram of a data input part of the semiconductormemory device according to one example of the present invention.

FIG. 3 shows a timing chart of a normal read/write operation of thesemiconductor memory device according to one example of the presentinvention.

FIG. 4 shows a block diagram of a test data write circuit of thesemiconductor memory device according to one example of the presentinvention (in a second test mode executed with some data input/outputterminals).

FIG. 5 shows a timing chart of a write test in the second test mode ofthe semiconductor memory device according to one example of the presentinvention.

FIG. 6 shows a timing chart of a read test in the second test mode ofthe semiconductor memory device according to one example of the presentinvention.

FIG. 7 shows a timing chart of a read/write operation in a first testmode of the semiconductor memory device according to one example of thepresent invention (in a normal read/write test mode).

FIG. 8 shows a flow chart of a method for testing the semiconductormemory device according to one example of the present invention.

FIG. 9 shows an overall block diagram of a semiconductor memory deviceaccording to another example of the present invention.

FIG. 10 shows a block diagram of a data input part of the semiconductormemory device according to another example of the present invention.

FIG. 11 shows a timing chart of a burst read/write test of thesemiconductor memory device according to another example of the presentinvention.

PREFERRED MODES OF THE INVENTION

Exemplary embodiments of the present invention will be hereinafterdescribed with reference to the attached drawings as needed.

As shown in FIGS. 1 and 9, a semiconductor memory device (100, 200)according to one exemplary embodiment of the present inventioncomprises: data input/output terminals (DQ0 to DQ31); a memory cellarray 122; and a data latch circuit 111 (see FIGS. 2 and 10 for details)for temporarily latching data captured from the data input/outputterminals (DQ0 to DQ31) and writing the data in the memory cell array122 with a delay in a normal write operation. The semiconductor memorydevice has a test mode (see FIG. 7 for the timing of an internal DQSsignal) in which the data latch circuit 111 latches data read to thedata input/output terminals (DQ0 to DQ31) in a read operation and writespreviously latched data in the memory cell array 122 without newlylatching data from the data input/output terminals (DQ0 to DQ31) in awrite operation.

Namely, in the test mode, the data read from the memory cell array 122to the input/output terminals (DQ0 to DQ31) is latched in the data latchcircuit 111 and the latched data in the data latch circuit is written inthe memory cell array again. Thus, by writing initial values in thememory cell array 122 in advance by a certain method, a data read testfrom the memory cell array to the input/output terminals and a datawrite test from the input/output terminals to the memory cell array canbe conducted without probing all the input/output terminals.

As shown in FIGS. 1 and 9, the semiconductor memory device (100, 200)according to one exemplary embodiment of the present invention maycomprise an input circuit 112 for sending data from the datainput/output terminals (DQ0 to DQ31) to the data latch circuit 111. Theinput circuit 112 may be configured to turn on in a normal writeoperation, turn off in a normal read operation (see FIG. 3 for RED andWRT commands and the timing of a DQ/DQS input circuit enable signal). Inthe test mode, the input circuit 112 may be configured to turn on in aread operation and turn off in a write operation (see the timing chartin FIG. 7).

In accordance with the above structure, even when all the datainput/output terminals are not probed, input circuits relating toinput/output terminals that are not probed can also be tested.

Also, as shown in FIGS. 1 and 9, according to the semiconductor memorydevice of one exemplary embodiment of the present invention, thesemiconductor memory device (100, 200) may further comprise an internaldata strobe signal generation circuit (701, 1001) and be structured sothat data captured from the data input/output terminals (DQ0 to DQ31) islatched in the data latch circuit 111 in synchronization with a datastrobe signal DQSn supplied from the outside in a normal write operation(see FIG. 3 for the timing of the DQ and DQS signals in a writeoperation) and that, in a read operation in the test mode, data read tothe data input/output terminals (DQ0 to DQ31) is latched insynchronization with an internal data strobe signal (702, 1007)generated by the internal data strobe signal generation circuit (701,1001) (see FIG. 7 for timing of the DQ and internal DQS signals in awrite operation).

In accordance with the above structure, since the internal data strobesignal generation circuit is provided, data read from the memory cellarray 122 can be latched in the data latch circuit 111 without supplyingany data strobe signal from the outside in a read operation.

In addition, as shown in FIG. 9, the semiconductor memory deviceaccording to one exemplary embodiment of the present invention mayfurther comprise, in the test mode, a FIFO circuit 1003 for temporarilycapturing data read by a burst operation from the memory cell array 122to the input/output terminals (DQ0 to DQ31) and a clock generationcircuit 1001 for generating a clock 1008 for capturing data into theFIFO circuit 1003 and sending the data captured into the FIFO circuit1003 toward the memory cell array.

In accordance with the above structure, since data read by a burstoperation from the memory cell array 122 to the input/output terminals(DQ0 to DQ31) is temporarily captured by the FIFO circuit 1003, the dataread by the burst operation can be written in the memory cell array 122again.

Furthermore, as shown in FIGS. 1 and 9, the semiconductor memory deviceaccording to one exemplary embodiment of the present invention may be asynchronous semiconductor memory device comprising: data input/outputterminals (DQ0 to DQ31); a memory cell array 122; and a data latchcircuit 111 for temporarily latching data captured from the datainput/output terminals in synchronization with a data strobe signal DQSnsupplied from the outside and writing the data in the memory cell arraywith a delay when a normal write command is executed. The synchronoussemiconductor memory device may further comprise an internal data strobesignal generation circuit (701, 1001) and a test mode in which the datalatch circuit 111 latches data read to the data input/output terminals(DQ0 to DQ31) in synchronization with an internal a data strobe signal(702, 1007) generated by the internal data strobe signal generationcircuit (701, 1001) when a read command is executed and writes thepreviously latched data in the memory cell array 122 without newlylatching data from the data input/output terminals (DQ0 to DQ31) when awrite command is executed (see the timing chart of FIG. 7).

In a synchronous semiconductor memory device such as a DDR-SDRAM thatperforms pipeline operation in synchronization with a clock suppliedfrom the outside, since a strobe signal (DQS signal) for capturing datafrom the data input/output terminals (DQ0 to DQ31) is not supplied fromthe outside when a read command is executed, the internal data strobesignal generation circuit (701, 1001) may be provided.

Further, as shown in FIGS. 1 and 9, the semiconductor memory deviceaccording to one exemplary embodiment of the present inventioncomprises: data input/output terminals (DQ0 to DQ31); a memory cellarray 122; and a data latch circuit 111 for temporarily latching datacaptured from the data input/output terminals and writing the data inthe memory cell array later. The semiconductor memory device has: afirst command for latching data captured from the data input/outputterminals (DQ0 to DQ31) in the data latch circuit 111 in synchronizationwith a strobe signal DQSn supplied from the outside and writing thelatched data in the memory cell array in synchronization with aninternal clock (see the timing chart of FIG. 3 for the normal writecommand (WRT)); a second command for reading data from the memory cellarray 122 to the data input/output terminals (DQ0 to DQ31) and latchingthe read data in the data latch circuit 111 (see the timing chart ofFIG. 7 for the a read command (RED) in a first test mode); and a thirdcommand for writing data stored in the data latch circuit 111 in thememory cell array 122 without newly capturing data from the datainput/output terminals (DQ0 to DQ31) into the data latch circuit 111(see the timing chart of FIG. 7 for a write command (WRT) in the firsttest mode).

By providing the above first to third commands, in addition to a normalwrite operation, a read/write test using input/output circuits of datainput/output terminals can be executed.

Also, as shown in FIGS. 1, 8, and 9, a semiconductor memory device testmethod according to one exemplary embodiment of the present invention isa method for testing the semiconductor memory device (100, 200)comprising: a plurality of data input/output terminals (DQ0 to DQ31 inFIGS. 1 and 9); and a memory cell array (reference numeral 122 in FIGS.1 and 9) in which one address is composed of multiple bits that can beread/written in parallel with the use of the plurality of datainput/output terminals (DQ0 to DQ31). The device has a test mode inwhich data read in parallel from the multiple-bit memory cell array 122to the plurality of data input/output terminals (DQ0 to DQ31) is writtenin parallel in a multiple-bit address different from the read address.According to the test method, first and second data is written in firstand second regions, respectively, in the memory cell array in advance(steps S2 and S3 in FIG. 8), and using the test mode, the second dataread from the second region is written in the first region (step S6) andthe data is read from the first region after the second data is writtenin the first region (step S9).

In accordance with the above test method, since certain regions in thememory cell array are provided with initial values in advance, byreading the initial values in parallel from the memory cell array to thedata input/output terminals and writing the data in parallel in multiplebits in a different address again, a read/write test can be carried outwithout supplying write data from the data input/output terminals.

As shown in FIGS. 1, 8, and 9, according to the semiconductor memorydevice test method according to one exemplary embodiment of the presentinvention, the semiconductor memory device (100, 200) may furthercomprise, assuming that the above test mode is a first test mode, asecond test mode in which, among the plurality of the data input/outputterminals (DQ0 to DQ31), some of the terminals (DQ0, 8, 16, and 24), thenumber of which is smaller than the number of bits of the memory cellarray, are used to write data in the multiple bits (32 bits) of thememory cell array 122 in parallel and the multiple-bit data read inparallel from the multiple bits (32 bits) is read with the terminals(DQ0, 8, 16, and 24). The second test mode may be used for writing firstand second data in first and second region, respectively, in the memorycell array 122 in advance (steps S2 and S3 in FIG. 8) and reading datafrom the first region (step S9).

In accordance with the above method, for example, during waferinspection, by probing some of a plurality of data input/outputterminals, input/output circuits relating to the data input/outputterminals that are not probed can also be tested.

The above exemplary embodiments of the present invention will behereinafter described in detail based on examples with reference todrawings.

EXAMPLE 1

FIG. 1 shows an overall block diagram of a semiconductor memory deviceaccording to an example 1. While the semiconductor memory deviceaccording to the example 1 is a DDR-SDRAM, the present invention is notmerely limited thereto. In FIG. 1, a semiconductor memory device(semiconductor memory chip) 100 comprises a memory core circuit unit 145and an output circuit unit 113. Power is supplied to the memory corecircuit unit 145 and the output circuit unit 113 via a VDD terminal anda VDDQ terminal, respectively. The semiconductor memory device 100further comprises: data input/output terminals DQ0 to DQ31; a data masksignal input terminal DMn (n is 0 to 3, for example); a data strobesignal input/output terminal DQSn (n is 0 to 3, for example); a clocksignal input terminal CLK; a command input terminal CMD; and an addressinput terminal ADD, among which, for example, the command input terminalCMD may be commonly used with another terminal. In addition, thesemiconductor memory device further comprises a memory cell array 122, arow decoder 116, and a column decoder 117, as well as an input circuit112, a data latch circuit 111, a data amplifier circuit 107, an outputdata buffer circuit 108, and the like that input and output data betweenthe memory cell array 122 and the data input/output terminals DQ0 toDQ31. Also, the semiconductor memory device further comprises: a clockgeneration circuit 101 for generating an internal clock signal based ona CLK signal; an output clock generation circuit 104 for generating aclock relating to an operation for reading data from the memory cellarray 122 and outputting the data to the outside; and an input dataclock generation circuit 106 for generating a clock relating to anoperation for capturing data from the outside and writing the data inthe memory cell array.

Additionally, the semiconductor memory device further comprises: aninput command latch/decode circuit 102 for latching and decoding aninputted command; and a control logic circuit 105 for outputting asignal controlling each part of the semiconductor memory device 100based on command decode results and a clock signal. Also, the controllogic circuit 105 outputs a test signal 1 (400), a test signal 2 (700),and a DQ/DQS input circuit enable signal 135, which control test modesthat will be described in detail later.

Further, the semiconductor memory device comprises a test data latchcircuit 138 and a data comparison/determination circuit 137 used in asecond test mode in which 32-bit data is written in the memory cellarray 122 by using 4 data input/output terminals (DQ0, DQ8, DQ16, andDQ24) among 32 data input/output terminals (DQ0 to DQ31) and 32-bit datais read from the memory cell array 122 with the above 4 datainput/output terminals. Circuits relating to the test will be describedin detail in the following description regarding the operation.

Next, the operation of the semiconductor memory device according to theexample 1 will be described in the following order: a normal read/writeoperation; a read/write test mode operation using some of the datainput/output terminals (second test mode); and a read/write test modeoperation using normal input/output circuits (first test mode).

EXAMPLE 1 Normal Read/Write Operation

FIG. 3 shows a timing chart of a normal read/write operation when theburst length is 2 (BL2). As described above, since the semiconductormemory device of the example 1 is a DDR-SDRAM, the device executes aread/write operation according to the specifications thereof. Namely,first, prior to read/write commands, active commands (ACTs) for banks tobe accessed are issued. In this case, since data is read from a Bank 0and written in a Bank 1, an active command (ACT) is issued for eachbank, and a row line selected by a row address is activated.Subsequently, when a read command (RED) for the Bank 0 is issued, memorycell data (D1 and D2) selected by a column address is sent from thememory cell array 122 in FIG. 1 to the data amplifier circuit 107, whichamplifies the data and then sends the data as internal read data 131 tothe output data buffer circuit 108. The internal read data (D1 and D2)131 is alternately outputted to the data input/output terminals (DQterminals) by the output clocks 123 generated by the leading andtrailing edges of the clock at a cycle T8. Further, from the DQSterminal, a low-level signal is outputted by the output clock 123 insynchronization with the leading edge of the clock at a cycle T7, andhigh- and low-level signals are alternatively outputted by the outputclocks 123 similarly generated by the leading and trailing edges of theclock at the cycle T8. Since the DQ and DQS terminals are controlled bythe output clocks 123 and output data simultaneously in a readoperation, the signals change at the same timing.

Next, when a write command (WRT) for the Bank 1 is issued, the inputcircuit 112 is enabled by the DQ/DQS input circuit enable signal 135 andcaptures external DQ/DQS signals. In synchronization with the clocksignal at a cycle T12, a DQS signal and a DQ signal (D3 and D4) havingthe center of the effective period thereof aligned to the leading andtrailing edge of the DQS signal are supplied from the outside. Further,the DQ signal is captured in the data latch circuit 111 by an internalDQS signal 702 generated by an internal DQS timing generation circuit701 based on the DQS signal supplied from the outside.

FIG. 2 shows configurations of the input circuit 112, the data latchcircuit 111, the data clock synchronization circuit 110, and theinternal DQS timing generation circuit 701. In a normal write operation,since the TEST signal 2 (700) is at a low level, the internal DQS signal702 is approximately in phase with the DQS signal. The DQ signal (D3 andD4) captured in the data latch circuit 111 by the internal DQS signal702 is inputted to the clock synchronization circuit 110 as latch dataEven and Odd 132, and the signal is then latched by the input data clock126 generated by the CLK signal at a cycle T13 in the data clocksynchronization circuit 110. Subsequently, the timing of the signal isaligned to the CLK signal, and is then written as clock synchronizationdata Even and Odd 133 in the memory cell array 122 via a data switchingcircuit 136 and the write buffer circuit 109. As described above, in awrite operation, the DQ signal is inputted prior to the DQS signal by ¼CLK cycle so that the DQ signal can be latched by the DQS signalinternally.

EXAMPLE 1 A Read/Write Test Mode Using Some of the Data Input/OutputTerminals (Second Test Mode)

Next, the operation of a second test mode in which a read/write test isexecuted on the memory cell array with some of the data input/outputterminals DQ0 to DQ31 is described. FIG. 5 shows a timing chart of awrite test in the second test mode of the example 1. In the second testmode, as described above, given DQ terminals alone are used to inputwrite data. In the block diagram of the DRAM of FIG. 1, DQ0, DQ8, DQ16,and DQ24 terminals are used as test-mode DQ terminals. Also, in thesecond test mode, since the DQS terminal is not used either, the DQsignal having the center of the effective period aligned to the leadingedge of the CLK signal is inputted, and is then latched by the inputdata clock 126 generated by the CLK signal in the test data latchcircuit 138.

FIG. 4 shows a block diagram of a portion relating to an operation forwriting a data signal inputted from the DQ terminals DQ0, 8, 16, and 24used in the second-test-mode in the memory cell array. As describedabove, the data signal inputted from the DQ terminals DQ0, 8, 16, and 24is latched in the test data latch circuit 138 by the input data clock126 generated by the CLK signal, and the signal is then inputted to thedata switching circuit 136 as internal test data 140. In the second testmode, the TEST signal 1 (400) is at a high level, and the data isinputted through a path involving internal test data 140, unlike thedata input path used in a normal operation involving individual DQterminals. Further, 4 data DQ0, 8, 16, and 24 are sequentially assignedto the input corresponding to each DQ terminal, so that data patterns inconsideration of physical arrangement of memory cells in the memory cellarray can be written. Namely, the data switching circuit 136 isconnected so that data inputted from any of the 4 terminals DQ0, 8, 16,and 24 is written in the 32 bits of the memory cell array that can beread/written simultaneously. The data outputted from the switchingcircuit 136 is inputted to the write buffer circuit 109 as internalwrite data 141 and written in the memory cell array 122.

FIG. 6 shows a timing chart of a read operation in the second test mode.In the second test mode, the data comparison/determination circuit 137compares data simultaneously read to the 4 terminals DQ0, 8, 16, and 24from the corresponding multiple bits in the memory cell array 122 todetermine whether all the data matches, thereby making a decision topass or fail. When a read command (RED) is issued after an activecommand (ACT), memory cell data selected by a column address is sentfrom the memory cell array 122 in FIG. 1 to the data amplifier circuit107, which amplifies the data and then sends the data as internal readdata 131 to the data comparison/determination circuit 137. Comparison ismade for each DQ group in which the same internal test data 140 iswritten in the above write operation in the second test mode, and a datacomparison/determination result 139 is sent to the output data buffercircuit 108. The data comparison/determination result 139 is outputtedfrom the terminals DQ0, 8, 16, and 24 in the same cycle by the outputcontrol signal 124 outputted from the control logic circuit 105 inresponse to the read command.

As a result of the determination, a high-level signal is outputted whenthe data is determined to be “pass” and a low-level signal when the datais determined to be “fail.” Namely, in a write operation in the secondtest mode, since the same data must have been written in the bitscorresponding to the 4 bits DQ0, 8, 16, and 24 of thesimultaneously-readable/writeable 32-bit data in the memory cell array,if each of the bit data corresponding the DQ0, 8, 16, and 24 of the32-bit data simultaneously read from the memory cell array 122 is thesame in the read operation, a high-level signal is outputted from thetest DQ terminals (DQ0, 8, 16, and 24). If not, a low-level signal isoutputted from the test DQ terminals (DQ0, 8, 16, and 24).

Thus, in accordance with the above second test mode, even in the case ofa semiconductor memory device (DRAM chip) having many data input/outputterminals (DQ terminals), the memory cell array thereof can be inspectedby probing only a small number of the DQ terminals. However, with thissecond test mode alone, it is impossible to conduct the DRAM read/writetest in a normal operation using all the above DQ terminals.

EXAMPLE 1 A Read/Write Test Mode Using Normal Input/Output Circuits(First Test Mode)

In the above test using the second test mode, input/output circuitsrelating to the data input/output terminals other than the test-mode DQterminals 0, 8, 16, and 24, such as the input circuit 112, the datalatch circuit 111, the data clock synchronization circuit 110, theoutput data buffer circuit 108, the output circuit unit 113, and wiringsconnecting these circuits, are not tested. In accordance with a firsttest mode described below, input/output circuits relating to the datainput/output terminals that are not probed can also be tested duringwafer inspection.

FIG. 7 shows a timing chart of a read/write test mode using normalinput/output circuits (first test mode). In FIG. 7, first, prior toread/write commands, active commands (ACTs) for banks to be accessed areissued. In this case, since data is read from a Bank 0 and written in aBank 1, an active command (ACT) is issued for each bank, and a row lineselected by a row address is activated. Subsequently, when a readcommand (RED) for the Bank 0 is issued, memory cell data (D1 and D2)selected by a column address is sent from the memory cell array 122 inFIG. 1 to the data amplifier circuit 107, which amplifies the data andthen sends the data as internal read data 131 to the output data buffercircuit 108. The internal read data (D1 and D2) 131 is alternatelyoutputted to the DQ terminals by the output clocks 123 generated by theleading and trailing edges of the clock at the cycle T8. Further, fromthe DQS terminal, a low-level signal is outputted by the output clock123 in synchronization with the leading edge of the clock at the cycleT7, and high- and low-level signals are alternately outputted by theoutput clocks 123 similarly generated by the leading and trailing edgesof the clock at the cycle T8.

In this first test mode, the DQ/DQS input circuit enable signal 135 isturned on by the read command, and the input circuit 112 is enabled tocapture DQ/DQS signals. In a read operation, since DQ and DQS signalsare simultaneously outputted by the output clocks 123, they are at thesame timing. Since the TEST signal 2 (700) is at a high level and theinternal DQS signal 702 is generated via a delay element, the latchtiming of the internal DQS signal 702 is secured with respect to the DQsignal in the data latch circuit 111. Thus, the internal DQS signal 702can properly capture the DQ signal (D1 and D2). Next, when a writecommand (WRT) for the Bank 1 is issued, the DQ signal (D1 and D2)captured in the data latch circuit 111 is latched in the data clocksynchronization circuit 110 as latch data Even and Odd 132 by the inputdata clock 126 generated by the CLK signal at a cycle T10. The timing ofthe latch data Even and Odd 132 is aligned to the CLK signal, and thedata is then written in the memory cell array 122 as clocksynchronization data Even and Odd 133 via the data switching circuit 136and the write buffer circuit 109.

Namely, in a normal read/write operation, when a write command isexecuted, the DQ/DQS input circuit enable signal 135 is turned on, theinput circuit 112 is enabled, and data supplied from the datainput/output terminals is captured. When a read command is executed, theDQ/DQS input circuit enable signal 135 remains turned off and the inputcircuit 112 remains disenabled. In addition, when a write command isexecuted, the data latch circuit 111 latches data outputted from theinput circuit 112. The data latch circuit 111 does not latch the datawhen a read command is executed.

In contrast, in the first test mode, when a read command is executed,the DQ/DQS input circuit enable signal 135 is turned on and the inputcircuit 112 is enabled to capture data from the data input/outputterminals. When a write command is executed, the input circuit 112remains turned off and it does not capture data supplied from the datainput/output terminals. Also, the data latch circuit 111 latches dataoutputted from the input circuit 112 when a read command is executed.The data latch circuit 111 does not latch the data when a write commandis executed.

As shown in FIG. 7, a write command (WRT) is captured by the leadingedge of the clock at the cycle T8, and thereafter, data is latched inthe data latch circuit 111 by the edges of the internal DQS signal 702attributable to execution of the read command (RED). However, this isdue to pipeline processing in which a command is processed with a delayfrom capture to execution. As described above, in the first test mode,execution of a write command does not enable the input circuit 112 orcause the data latch circuit 111 to latch data from the datainput/output terminals.

Also, when a normal write command is executed, a data strobe signal issupplied from the data strobe terminal (DQS terminal) in accordance withthe timing of data supplied from the data input/output terminals (DQterminals) on the memory controller side. Thus, it is only necessary toallow the data latch circuit 111 to latch data in synchronization withthe data strobe signal (DQS signal) supplied from the outside. However,in the first test mode, the timing at which data read from the memorycell array 122 to the data input/output terminals (DQ0 to DQ31) islatched in the data latch circuit 111 is not given from the outside.Thus, by causing the internal DQS timing generation circuit 701 in FIG.2 to generate an internal DQS signal lagging behind the DQ signal by ¼cycle, data read from the memory cell array 122 is latched in the datalatch circuit 111.

As described above, by using the first test mode, data read from memorycells can be outputted from DQ terminals, the output data can beinputted to the input circuit, and the data can be written in the memorycells again, without supplying signals to the DQ and DQS terminals fromthe outside.

EXAMPLE 2

Next, a semiconductor memory device test method of an example 2 will bedescribed. The example 2 is a method for testing the semiconductormemory device 100 by using the first and second test modes described inthe example 1. FIG. 8 is a flow chart of the test method of the example2. Based on the flow chart in FIG. 8, the operation of the input/outputcircuits can be checked without probing all the DQ terminals duringwafer inspection. First, the semiconductor memory device 100 is set inthe second test mode, which is used to conduct a read/write test usingsome of the data input/output terminals (step S1). The device may be setin the second test mode by applying a voltage that is not used in anormal operation to a certain terminal or by executing a certaincommand. Alternatively, a known method may be used to set the device inthe test mode. Next, a data pattern 0101 is written in the memory cellsof an address X=#000 to #0FF (step S2), and an inverse data pattern 1010is written in the memory cells of an address X=#100 to #1FF (step S3).

Next, the second test mode is cancelled (step S4), and the device is setin the first test mode (step S5). The data pattern 1010 written inX=#100 to #1FF is read from the memory cells to the terminals DQ0 toDQ31, and the data pattern is written in the memory cells of the addressX=#000 to #0FF by a write command inputted subsequently (step S6). Next,the second test mode is set again (steps S7 and S8). The rewrittenmemory cell data of the address X=#000 to #0FF is read and compared, soas to determine whether the input/output circuits have operated properly(step S9).

The same procedure is carried out for the address X=#100 to #1FF.Namely, after the step S9, in the second test mode, the data pattern1010 is written in the address X=#000 to #0FF and the inverse datapattern 0101 in the address X=#100 to #1FF (steps S10 and S11). Next,the mode is switched to the first test mode (steps S12 and S13), thedata in the address X=#000 to #0FF is read and written in the memorycells of the address X=#100 to #1FF (step S14). The mode is switched tothe second test mode again (steps S15 and S16), and the rewritten memorycell data of the address X=#100 to #1FF is read and compared (step S17).In accordance with this procedure, a test using input/output circuits ina normal operation is conducted on all cells of a DRAM.

In accordance with the above procedure, in the wafer inspection process,by only probing some of the data input/output terminals used in thesecond test mode, input/output circuits relating to the other datainput/output terminals that are not probed can also be tested. Also, inthe above example 2, while the first test mode is used in combinationwith the second test mode, an effective test can be carried out withoutcombining the first test mode with the second test mode. For example, itis possible to conduct a self-diagnostic test after the semiconductormemory device is incorporated in a system, by initializing the memorycell array with a normal write command, repeating read and writeoperations in the first test mode, transferring data sequentially, andreading the final results with a normal read command.

Further, in the example 2, a step for switching the test mode isprovided between reading/writing in the first test mode andreading/writing in the second test mode. However, reading/writing may beautomatically switched between the normal mode, the first test mode, andthe second test mode, after receiving a command of a different mode.

EXAMPLE 3

The above example 1 is an effective example in cases in which only 2-bitdata is inputted/outputted through read/write commands. While normaldata output includes a burst mode for sequentially inputting/outputting4, 8, or 16-bit data, if more than 2-bit data is sequentially outputtedin the example 1, the latch data Even and Odd 132 outputted from thedata latch circuit 111 is caused to be updated, which makes itimpossible to rewrite the data read to the data input/output terminals,and therefore a test cannot be conducted properly. In the example 3, inorder to enable a test in a burst operation for outputting more than2-bit data, a FIFO circuit for receiving and storing data in a readoperation is provided. The FIFO circuit sequentially stores the DQ datain response to the input of the data strobe signal DQS in a readoperation, and the circuit sequentially sends the data therein to thedata CLK synchronization circuit in response to the input data clock ina write operation.

FIG. 9 shows a block diagram of an overall semiconductor memory deviceof the example 3, and FIG. 10 shows a block diagram of a data input partof the device. When FIG. 9 is compared with FIG. 1, which shows a blockdiagram of an overall semiconductor memory device of the example 1, itis seen that the example 3 is different from the example 1 in that aninternal DQS timing/clock generation circuit 1001 is used instead of theinternal DQS timing generation circuit 701 and that a test data FIFOcircuit 1003 is provided between the data latch circuit 111 and the dataclock synchronization circuit 110. The example 3 is generally the sameas the example 1 in other aspects. Portions that are almost the same asthose in example 1 are denoted by the same reference characters and thedescriptions thereof are omitted.

FIG. 11 shows a timing chart of a burst read/write test conducted on asemiconductor memory device 200 of the example 3. In the timing chart ofFIG. 11, first, prior to read/write commands, active commands (ACTs) forbanks to be accessed are issued. Subsequently, when a read command (RED)for the Bank 0 is issued, memory cell data (D1 and D2) selected by acolumn address is sent from the memory cell array 122 in FIG. 9 to thedata amplifier circuit 107, which amplifies the data and then sends thedata as internal read data 131 to the output data buffer circuit 108.The internal read data (D1 and D2) 131 is alternately outputted to theDQ terminals by the output clocks 123 generated by the leading andtrailing edges of the clock at the cycle T8. Further, high- andlow-level DQS signals are alternately outputted from the DQS terminalsby the output clocks 123. The DQ/DQS input circuit enable signal 135 isturned on by the read command, and the input circuit 112 is enabled tocapture DQ/DQS signals.

As in the example 1, since the TEST signal 2 (1000) is caused to be at ahigh level and an internal DQS signal 1007 is generated via a delayelement, the latch timing of the internal DQS signal 1007 is securedwith respect to the DQ signal in the data latch circuit 111, and the DQsignal (D1 and D2) can be captured properly. Next, after the cycle T7 atwhich the read command is inputted, memory cell data (D3 to D8) of aninternally-generated address is read by 2 bits at a cycle from aninputted column address to the DQ terminals. The data thus outputted isreceived by the input circuit 112 and is then sequentially captured inthe data latch circuit 111. Latch data Even and Odd 1032 outputted fromthe data latch circuit 111 is sequentially stored in the test data FIFOcircuit 1003 by a FIFO control signal 1008 generated by the DQS signal.When the 8-bit data is outputted at a cycle T12, an FIFO output 1004represents initial data (D1 and D2).

Next, when a write command (WRT) for the Bank 1 is issued, the FIFOcontrol signal 1008 is generated by an input data clock 1002, not by theDQS signal. The data in the FIFO circuit is then sequentially latched ina data clock synchronization circuit 1005 at each cycle, starting withthe initial data (D1 and D2). The data having the timing thereof alignedto the CLK signal is sequentially written in the memory cell array 122at each cycle as the clock synchronization data Even and Odd 133 via thedata switching circuit 136 and the write buffer circuit 109.

Thus, in accordance with the burst read/write test mode of the example3, without supplying signals to the DQ and DQS terminals from theoutside, the burst data sequentially read from memory cells is outputtedfrom the DQ terminals, the input circuit receives the outputted data,and the data is written in the memory cells again. Also, with thesemiconductor memory device of the example 3, by replacing theread/write operation in the first mode in the example 2 with the burstread/write operation, input/output circuits relating to the datainput/output terminals that are not probed can also be tested in theburst read/write operation.

The circuit configuration of the test data FIFO circuit 1003 isarbitrary as long as it is a buffer circuit having a function of storingthe latch data 1032 in synchronization with the FIFO control signal 1008and outputting data to the FIFO output 1004 in synchronization with theFIFO control signal 1008, with the initially inputted data first. Forexample, a FIFO circuit using a dual-port SRAM may be used.

Also, in the examples 1 and 3, test-related control signals, such as theTEST signal 1 (400), the TEST signal 2 (700, 1000), and the DQ/DQS inputcircuit enable signal 135, are outputted from the control logic circuit105. However, a dedicated control circuit for test purposes may beprovided to output control signals relating to the above tests. Furtheralternatively, other circuits may output control signals relating to thetests.

In the present invention, the following modes are possible.

(Mode 1):

As mentioned as the first aspect.

(Mode 2):

The semiconductor memory device may further comprise an input circuitconfigured to send data from the data input/output terminal to the datalatch circuit, the input circuit turning on in a normal write operationand turning off in a normal read operation, wherein, in the test mode,the input circuit turns on in a read operation and turns off in a writeoperation.

(Mode 3):

The semiconductor memory device may further comprise an internal datastrobe signal generation circuit, wherein, in a normal write operation,data captured from the data input/output terminal is latched in the datalatch circuit in synchronization with a data strobe signal supplied fromthe outside, and, in a read operation in the test mode, data read to thedata input/output terminal is latched in synchronization with aninternal data strobe signal generated by the internal data strobe signalgeneration circuit.

(Mode 4):

The semiconductor memory may further comprise, in the test mode, a FIFOcircuit that temporarily captures data read by a burst operation fromthe memory cell array to the input/output terminal; and a clockgeneration circuit that generates a clock capturing data into the FIFOcircuit and a clock sending the data captured into the FIFO circuittoward the memory cell array.

(Mode 5):

As mentioned as the second aspect.

(Mode 6):

The synchronous semiconductor memory device may further comprise aninput circuit configured to send data from the data input/outputterminal to the data latch circuit, the input circuit turning on when anormal write command is executed and turning off when a normal readcommand is executed, wherein, in the test mode, the input circuit turnson when a read command is executed and turns off when a write command isexecuted.

(Mode 7):

The synchronous semiconductor memory device may comprise, in the testmode, a buffer circuit that temporarily captures data read by a burstoperation from the memory cell array to the input/output terminal; and aclock generation circuit that generates a clock capturing data into thebuffer circuit and a clock sending data captured into the buffer circuittoward the memory cell array in the order of capture.

(Mode 8):

As mentioned as the third aspect.

(Mode 9):

The semiconductor memory device may further comprise, a FIFO circuit; afourth command for sequentially storing data read by a burst operationfrom the memory cell array to the input/output terminal in the FIFOcircuit; and a fifth command for writing data stored in the FIFO circuitin the memory cell array by a burst operation, without newly capturingdata from the data input/output terminal.

(Mode 10):

As mentioned as the forth aspect.

(Mode 11):

The semiconductor memory device may further comprise, assuming that theabove test mode is a first test mode, a second test mode in which partof the plurality of data input/output terminals, the number of which issmaller than the number of bits of the memory cell array, is used towrite data in the multiple bits of the memory cell array in parallel andread the multiple-bit data from the multiple bits in parallel. Writingfirst and second data in first and second region, respectively, in thememory cell array in advance and reading data from the first region areimplemented with the second test mode.

(Mode 12):

After the test in which data is read from the first region, the seconddata is written in the first region with the second test mode, the firstdata is written in the second region with the second test mode, thefirst data read from the first region is written in the second regionwith the first test mode, and a read test is conducted on the secondregion with the second test mode.

(Mode 13):

The semiconductor memory device may comprise, in the first test mode, afunction of writing by a burst operation data read by a burst operationfrom the memory cell array in a region having an initial addressdifferent from the address read by the burst operation. Writing thesecond data read from the second region in the first region with thefirst test mode and writing the first data read from the first region inthe second region with the first test mode are implemented with thefunction of burst reading and burst writing.

It should be noted that other objects, features and aspects of thepresent invention will become apparent in the entire disclosure and thatmodifications may be done without departing the gist and scope of thepresent invention as disclosed herein and claimed as appended herewith.

Also it should be noted that any combination of the disclosed and/orclaimed elements, matters and/or items may fall under the modificationsaforementioned.

1. A semiconductor memory device comprising: a data input/outputterminal; a memory cell array; and a data latch circuit configured totemporarily latch data captured from the data input/output terminal andwrite data in the memory cell array with a delay in a normal writeoperation, wherein the semiconductor memory device further comprises atest mode in which the data latch circuit latches data read to the datainput/output terminal in a read operation and writes previously latcheddata in the memory cell array without newly latching data from the datainput/output terminal in a write operation.
 2. The semiconductor memorydevice according to claim 1, further comprising an input circuitconfigured to send data from the data input/output terminal to the datalatch circuit, the input circuit turning on in a normal write operationand turning off in a normal read operation, wherein, in the test mode,the input circuit turns on in a read operation and turns off in a writeoperation.
 3. The semiconductor memory device according to claim 1,further comprising an internal data strobe signal generation circuit,wherein, in a normal write operation, data captured from the datainput/output terminal is latched in the data latch circuit insynchronization with a data strobe signal supplied from the outside,and, in a read operation in the test mode, data read to the datainput/output terminal is latched in synchronization with an internaldata strobe signal generated by the internal data strobe signalgeneration circuit.
 4. The semiconductor memory device according toclaim 1, further comprising, in the test mode, a FIFO circuit thattemporarily captures data read by a burst operation from the memory cellarray to the input/output terminal; and a clock generation circuit thatgenerates a clock capturing data into the FIFO circuit and a clocksending the data captured into the FIFO circuit toward the memory cellarray.
 5. A synchronous semiconductor memory device comprising: a datainput/output terminal; a memory cell array; a data latch circuitconfigured to temporarily latch data captured from the data input/outputterminal in synchronization with a data strobe signal supplied from theoutside and write data in the memory cell array with a delay when anormal write command is executed; and an internal data strobe signalgeneration circuit, wherein the semiconductor memory device furthercomprises a test mode in which the data latch circuit latches data readto the data input/output terminal in synchronization with an internaldata strobe signal generated by the internal data strobe signalgeneration circuit when a read command is executed and writes previouslylatched data in the memory cell array without newly latching data fromthe data input/output terminal when a write command is executed.
 6. Thesynchronous semiconductor memory device according to claim 5, furthercomprising an input circuit configured to send data from the datainput/output terminal to the data latch circuit, the input circuitturning on when a normal write command is executed and turning off whena normal read command is executed, wherein, in the test mode, the inputcircuit turns on when a read command is executed and turns off when awrite command is executed.
 7. The synchronous semiconductor memorydevice according to claim 5, comprising, in the test mode, a buffercircuit that temporarily captures data read by a burst operation fromthe memory cell array to the input/output terminal; and a clockgeneration circuit that generates a clock capturing data into the buffercircuit and a clock sending data captured into the buffer circuit towardthe memory cell array in the order of capture.
 8. A semiconductor memorydevice comprising: a data input/output terminal; a memory cell array; adata latch circuit configured to temporarily latch data captured fromthe data input/output terminal and write data in the memory cell arraylater; wherein the semiconductor memory device further comprises: afirst command for latching data captured from the data input/outputterminal in the data latch circuit in synchronization with a strobesignal supplied from the outside and writing latched data in the memorycell array in synchronization with an internal clock; a second commandfor reading data from the memory cell array to the data input/outputterminal and latching the read data in the data latch circuit; and athird command for writing data stored in the data latch circuit in thememory cell array without newly capturing data from the datainput/output terminal into the data latch circuit.
 9. The semiconductormemory device according to claim 8, further comprising, a FIFO circuit;a fourth command for sequentially storing data read by a burst operationfrom the memory cell array to the input/output terminal in the FIFOcircuit; and a fifth command for writing data stored in the FIFO circuitin the memory cell array by a burst operation, without newly capturingdata from the data input/output terminal.
 10. A semiconductor memorydevice test method, the device comprising: a plurality of datainput/output terminals; and a memory cell array in which one address iscomposed of multiple bits that can be read/written in parallel with theplurality of data input/output terminals, wherein the device furthercomprises a test mode in which data read in parallel from themultiple-bit memory cell array to the plurality of data input/outputterminals is written in parallel in multiple bits of an addressdifferent from the read address, and wherein the test is conducted bywriting first and second data in first and second regions, respectively,in the memory cell array in advance, using the test mode, writing thesecond data read from the second region in the first region, and readingthe data from the first region after the second data is written in thefirst region.
 11. The semiconductor memory device test method accordingto claim 10, the device further comprising, assuming that the above testmode is a first test mode, a second test mode in which part of theplurality of data input/output terminals, the number of which is smallerthan the number of bits of the memory cell array, is used to write datain the multiple bits of the memory cell array in parallel and read themultiple-bit data from the multiple bits in parallel, wherein writingfirst and second data in first and second region, respectively, in thememory cell array in advance and reading data from the first region areimplemented with the second test mode.
 12. The semiconductor memorydevice test method according to claim 11, wherein, after the test inwhich data is read from the first region, the second data is written inthe first region with the second test mode, the first data is written inthe second region with the second test mode, the first data read fromthe first region is written in the second region with the first testmode, and a read test is conducted on the second region with the secondtest mode.
 13. The semiconductor memory device test method according toclaim 12, wherein the semiconductor memory device comprises, in thefirst test mode, a function of writing by a burst operation data read bya burst operation from the memory cell array in a region having aninitial address different from the address read by the burst operation,wherein writing the second data read from the second region in the firstregion with the first test mode and writing the first data read from thefirst region in the second region with the first test mode areimplemented with the function of burst reading and burst writing.